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Relaying barrier message

Reading the news feature on the problems with developing a 'moving block' signalling system for the Jubilee Line Extension (NCE 21 May)brought back memories of my time in the early 1980s, working for the then Greater London Council on another large and complex project, the Thames Barrier.

One of the underlying principles adopted at an early stage in the design of the Barrier was to use only proven technology and systems. I recall that this approach led to the use of Post Office relays (hundreds, possibly thousands of them) in the control systems for the operating machinery; this at a time when computer technology was advancing rapidly and there were those who believed the relay-based system should be scrapped at a late stage in the project and replaced with new technology.

The decision was taken to press on with the use of relays, even though it was recognised that they were certain to be replaced at some future date by electronics. In the event, the project was delayed for a number of other, well-documented reasons, but at least not because of the use of risky new technology!

I would not envy Hugh Doherty (a former colleague of mine) and his team having to take the difficult decision to temporarily abandon 'moving block' in favour of the traditional signalling system, in order to minimise delay to the JLE project. How he must wish he could, with the benefit of hindsight, have put the clock back a couple of years before taking it.

Gordon J Heath (M), 90 Catlins Lane, Pinner, Middlesex HA5 2BX.

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